Field of the Invention
Embodiments of techniques disclosed herein generally pertain to seismic exploration and, more particularly, to the imaging of seismic data.
Background of the Technology
This section of this document introduces information about and/or from the art that may provide context for or be related to the subject matter described herein and/or claimed below. It provides background information to facilitate a better understanding of the various aspects of the presently disclosed technique. This is a discussion of “related” art. That such art is related in no way implies that it is also “prior” art. The related art may or may not be prior art. The discussion in this section of this document is to be read in this light, and not as admissions of prior art.
Seismic surveying is the practice of studying subterranean formations from reflections by those formations of acoustic waves. This includes imparting acoustic waves into a natural environment so that they may enter the earth and travel through the subterranean geological formations of interest. During their travels through the formations, certain features of the formations will reflect the waves back to the surface where they are recorded.
The recorded reflections are then studied to ascertain information about those formations. The seismic data derived from the recorded reflections is processed to, for example, image the subterranean formations that generated the reflections in some cases. The images, and models derived from them, can help identify subsurface resources. Most notably, these resources may include fluid hydrocarbons such as petroleum and natural gas. The techniques may be applied to the location of other kinds of resources as well.
The study of the recorded reflections involves digitizing the recordings and then processing them as a seismic data set. Seismic data sets are very large even by modern computing standards. The processing is also computationally intensive. The industry therefore uses large, powerful computing systems with large, high capacity storage to perform this part of the analysis.
The analysis itself may take many forms depending upon the end use of the resultant product. Frequently, the analysis models the subterranean formation based on one or more of its physical attributes to image it for analysis. The model, or “image”, may or may not be rendered for human perception depending, again, on the end use. There are many techniques that are used in varying combinations as is well known and commonly practiced in the art.
One common technique used in imaging seismic data is known as data “migration”. One of the tools frequently used in migration is a “velocity model” (or more generally, a “subsurface attribute model”, which might also include anisotropy parameters, shear-wave velocity, density, etc) that is generated from the seismic data. A velocity model is a representation of the geological formation that can be used in analyses of various types, typically resulting in an image of the subterranean formation from which the seismic data were acquired. The quality of these images frequently depends upon the quality of the velocity model. A poor quality velocity model will yield a poor migration and, ultimately, a poor image.
Seismic image quality dependency on the migration velocity model becomes progressively higher as geological complexity increases. Advancement in more theoretically rigorous model estimation technologies such as waveform inversion will gradually improve model building capabilities over time to meet this challenge, but it is also important to realize that certain degrees of imperfection in the velocity models will always be expected, at least in the foreseeable future. There is therefore a need to adjust/improve images as part of the migration process to account for this imperfection, and furthermore to mitigate the inadequacy of the physics used at various stages in the data processing pipeline.
For example, in the Gulf of Mexico where salt is the dominant structural element, inadequate velocity models have long been recognized as one of the main obstacles to the delivery of good quality seismic images. Large fractions of the computing cycles devoted to velocity estimations are consumed by salt body delineations, often also involving a great deal of interpretation work. This labor-intensive workflow for the most part is centered around fine-tuning the details of the salt geometry, on a scale that is within the resolving power of seismic signals but is unfortunately out of the reach of the current velocity estimation tools.
The presently disclosed technique is directed to resolving, or at least reducing, one or all of the problems mentioned above. Even if solutions are available to the art to address these issues, the art is always receptive to improvements or alternative means, methods and configurations. Thus, there exists a need for techniques such as that disclosed herein.